linux-kernel - Re: [RFC PATCH v11 6/9] media: tegra: Add Tegra210 Video input driver

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Date:   Thu, 30 Apr 2020 22:47:47 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com, frankc@...dia.com,
        hverkuil@...all.nl, sakari.ailus@....fi, helen.koike@...labora.com
Cc:     sboyd@...nel.org, linux-media@...r.kernel.org,
        devicetree@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v11 6/9] media: tegra: Add Tegra210 Video input driver

30.04.2020 22:32, Sowjanya Komatineni пишет:
> 
> On 4/30/20 6:38 AM, Dmitry Osipenko wrote:
>> 30.04.2020 01:00, Sowjanya Komatineni пишет:
>>> +/**
>>> + * struct tegra_csi_ops - Tegra CSI operations
>>> + *
>>> + * @csi_streaming: programs csi hardware to enable or disable
>>> streaming.
>>> + * @csi_err_recover: csi hardware block recovery in case of any
>>> capture errors
>>> + *        due to missing source stream or due to improper csi input
>>> from
>>> + *        the external source.
>>> + */
>>> +struct tegra_csi_ops {
>>> +    int (*csi_streaming)(struct tegra_csi_channel *csi_chan, u8
>>> pg_mode,
>>> +                 int enable);
>> What about to split csi_streaming() into csi_start_streaming() /
>> csi_stop_streaming()?
>>
>> This will make tegra_csi_ops to be consistent with the tegra_ve_ops. A
>> separated start/stop operations are somewhat more natural to have in
>> general.
> 
> vi ops is for vb2_ops which has separate start/stop so has seperate
> start/stop for vi ops.
> 
> csi is subdev and csi ops is for v4l2_subdev_ops which as s_stream
> callback only.
> 
> So, created single stream function for csi to match same as subdev_ops.

It will be nicer to have separate ops for CSI, regardless of the
subdev_ops. It should be okay to have a single-combined ops if CSI
start/stop was trivial, but it's not the case here.

For example, the pm_runtime_put() shouldn't be invoked if stream's
stopping fails. The stopping can't fail for the current code, but this
could change in the future.

You could make csi_streaming to return void, telling explicitly that
this code can't fail. Then the combined OPS should be okay to have.